1. Field of the Invention
The present invention relates generally to peripheral device hubs and, more specifically, to Universal Serial Bus (USB) switching hubs.
2. Description of the Related Art
The Universal Serial Bus (USB) allows coupling of peripheral devices to a computer system. USB is a serial cable bus for data exchange between a host computer and a wide range of simultaneously accessible devices. The bus allows peripherals to be attached, configured, used, and detached while the host is in operation. For example, USB printers, scanners, digital cameras, storage devices, card readers, etc. may communicate with a host computer system over USB. USB based systems may require that a USB host controller be present in the host system, and that the operating system (OS) of the host system support USB and USB Mass Storage Class Devices.
USB devices may communicate over the USB bus at low-speed (LS), full-speed (FS), or high-speed (HS). A connection between the USB device and the host may be established via digital interconnect such as Interchip USB, ULPI, UTMI, etc., or via a four wire interface that includes a power line, a ground line, and a pair of data lines D+ and D−. When a USB device connects to the host, the USB device may first pull a D+ line high (the D− line if the device is a low speed device) using a pull up resistor on the D+ line. The host may respond by resetting the USB device. If the USB device is a high-speed USB device, the USB device may “chirp” by driving the D− line high during the reset. The host may respond to the “chirp” by alternately driving the D+ and D− lines high. The USB device may then electronically remove the pull up resistor and continue communicating at high speed. When disconnecting, full-speed devices may remove the pull up resistor from the D+ line (i.e., “tri-state” the line), while high-speed USB devices may tri-state both the D+ and D− lines.
A USB hub may be coupled to a USB host controller to allow multiple USB devices to be coupled to the host system through the USB host controller. In addition, other USB hubs may be coupled to the USB hub to provide additional USB device connections to the USB host controller.
Some dual role peripheral devices may include a slave controller and be capable of communicating with other peripheral devices coupled to them. For example, a dual role USB printer may be able to communicate directly with a USB camera to print pictures from the USB camera. The dual role USB printer may also be accessible (e.g., by a computer system) as a slave peripheral device. If a computer system and dual role peripheral device need to alternately access a peripheral device, the peripheral device may need to be unplugged from one device and coupled to the other. Prior art device switches may not work for high-speed peripheral devices. For example, mechanical switches may introduce too much capacitance or inductance to work with high-speed peripheral devices. High-speed peripheral devices also typically require smooth impedance to prevent ringing (mechanical switches introduce irregularities in the impedance that may cause ringing).
U.S. Patent Application Publication No. 20060059293 (application Ser. No. 10/940,406) and U.S. Patent Application Publication No. 20060056401 (application Ser. No. 11/100,299) describe a USB switching hub that can switch between upstream ports and downstream ports. A USB switching hub may be used in a system having a first host device (e.g., a computer system), wherein the switching hub may initially couple a plurality of peripheral devices to the first host device, and where it is desired to switch the peripheral devices to couple to a second host device when the second host device is attached to the system. In this instance, an easy, intuitive method for the end user to actuate the switching of peripherals between two hosts is desired. In other words, a method is desired that allows the switching of peripherals between two hosts, where peripherals are usually attached to one host and are switched to a second host when the second host is attached to the system.
Other corresponding issues related to the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.